In recent years, the volume of waste, such as municipal waste containing a large amount of raw garbage, has increased greatly, and it has become extremely difficult to secure adequate landfill space. The increase in waste has become a serious social problem, particularly in urban areas.
In order to solve this problem, and also to address other global environmental issues, systems which burn waste, and utilize the heat produced by its combustion, have been introduced.
FIG. 4 shows a waste gasification power generation system disclosed in Unexamined Japanese Patent Publication No. 118124/1999, which is one example of the above-mentioned combustion energy utilization systems.
In this waste gasification power generation system 100, waste 102 is fed from a waste supplier into a fluidized bed gasification furnace 101. Partially oxidized gas, generated in the gasification furnace 101, is sent from a gas discharge port to a cyclone separator 103, in which it is separated into not-yet-burnt char 105, dust 104, and combustible gas 120.
The not-yet-burnt char 105 is recycled, as a combustible, into the gasification furnace 101. The dust 104 is processed in an ash fusion furnace in the same way as the not-yet-burnt part. The combustible gas, from which the solid content has been separated, is introduced, through path 120, into a burner 110 through an air pre-heater (not shown). Part of air heated in the air preheater is sent into the burner 110, and the remainder is sent into an air scattering pipe (not shown) as fluidization air. The combustible gas, sent to the burner 110 through path 120, is burned, and generates combustion gas at a high temperature. The high temperature combustion gas generates steam in a boiler 111, and, after removal of dust by means of a bag filter 114, the gas is released to the atmosphere through a chimney 115 after going through an induced draft fan (not shown). Before the gas reaches the bag filter 114, slaked lime is added from a silo (not shown) to remove salt and reduce acidity. Steam, generated in the boiler 111, generates power by driving a steam turbine 113.
As waste is thrown directly into the conventional fusion furnace, a large amount of fuel oil was required in order to raise the temperature to 1500 degrees Celsius. In addition, because the internal pressure in the furnace is increased on order to produce fusion, the structure of the equipment becomes more complex.
The more complex equipment is very difficult to operate, and consequently it was necessary for the manufacturer to provide skilled operators, resulting in excessive labor cost.
Moreover, if the waste has a high moisture content, it is difficult to raise its temperature to 1500 degrees Celsius.
Thus, a conventional fusion furnace has a high equipment cost due to its complex structure, as well as a high operating cost due to excessive fuel requirements and the need for highly skilled labor.
The conventional fusion furnace eliminates dioxin generated from incinerated remainders such as bottom ash or fly ash by adsorbtion into activated carbon or slaked lime.
Consequently, wastes containing dioxin have continued to increase and have become a problem.
Moreover, although the waste power generating system 100 of FIG. 4 is designed to eliminate burnt ash in the cyclone separator 103, and to supply only gasified gas to the combustion furnace, the uptake efficiency of ash within the cyclone separator is around 90%, and therefore it is unavoidable that some ash will be carried into the boiler 111.
The burnt ash contains a large amount of chlorides (NaCl, KCl) and sulfates (Na2SO4, K2SO4), and furthermore, the combustion gas contains a large amount of HCl gas, for example, up to 1000 ppm. Intense high temperature corrosion occurs due to reaction between compounds having a low melting point below 500 degrees Celsius, and HCl contained in the gas within the heat exchanger within the boiler. Therefore, in the conventional waste power generation system the steam temperature is generally set to a low level, e.g. as low as below 400 degrees Celsius. This results in low power generation efficiency.
Attempts have been made to improve power generation efficiency by using a dedusting apparatus, filtration, or the like, between the furnace and the heat exchanger to increase the ash take-up efficiency in the combustion gas. However satisfactory results could not be obtained with these measures.
In addition, with the increasing call for effective use of resources in recent years, there has been a demand for the utilization of biomass. However, when using woody biomass such as scrap wood, or live biomass such as raw garbage, major problems were encountered, such as securing stable amounts, property changes, and high moisture content. In particular, although it is possible to secure stable collection of live biomass, as enormous amounts are disposed of, it is difficult to secure stable collection of woody biomass.
In view of the above problems, the invention combines a carbonizer and gasifying fusion furnace technology to provide a waste carbonizing and energy utilization system having high efficiency, and enables the utilization of all kinds of waste biomass, including raw garbage with a high moisture content, without producing burnt ash, which is a cause of intense high temperature corrosion.